In the process of electrostatographic copying, a plate comprising a layer of photoconductive insulating material is electrostatically charged in the dark in order to apply a uniform charge to its surface. The charged plate is then exposed to activating radiation in imagewise configuration to selectively dissipate the charge in the illuminated areas while leaving behind a latent electrostatic image corresponding to the non-illuminated areas. The latent image is then developed by depositing finely divided electroscopic marking materials, commonly referred to as toner, on the surface of the plate. The toner particles are electrostatically attracted to the latent image and can be transferred to a receiving member such as paper in imagewise configuration. Thermal fusing of the toner into the receiving member provides a permanent copy. This concept, which was originally disclosed by Carlson in U.S. Pat. 2,297,691, has been further amplified in many related patents in the field.
In the self-adhesive drafting film market it is standard procedure to use sheets consisting of a film support coated on the back with a pressure sensitive adhesive and on the front with a matte coating. A second film having a release layer on its top surface is applied to the back of the first film. A release layer is applied to the second film so that upon its removal the adhesive layer is exposed. These films are used for making corrections in engineering drawings by marking the film's matte surface with the desired material, cutting out the marked portion of the drafting film, removing the release liner and sticking the so-prepared portion of the film on the drawing. In this manner, corrections can be made quickly without requiring erasure of the original drawing. In another use of these films, features which are used frequently in the drawing can be imprinted on the film and the drawing prepared using the feature from the self-adhesive drafting film. An example of this utility involves the preparation of circuit diagrams requiring repeated usage of the symbol for a diode. Rather than draw the symbol repeatedly; the draftsman can obtain a sheet of film already imprinted with a plurality of the symbols and easily apply them to the drawing in the appropriate places. This is accomplished by simply cutting out the symbol, removing the release liner to expose the adhesive and applying the symbol to the circuit diagram in the desired location. In some applications the entire sheet of film is used rather than just a cut out portion of it.
The matte coating of the drafting film can be imaged in any number of ways including offset printing. A convenient way to form this image is by means of an electrostatographic copier. However, imaging of conventional film to film pressure sensitive adhesive drafting films in electrostatographic copiers has proven problematical. This is the case because these films presently available to not possess the requisite surface conductivity to be easily processed in such copiers. In addition, the films are not readily manipulated by automatic sheet feeding devices in the copier because providing a stack of sheets with the back film of one sheet in contact with the matte coating of the sheet under it tends to cause the sheets to stick together and not feed one at a time, if at all.
It would be desirable, and it is an object of the present invention, to provide a novel film to film self adhesive drafting film which is suitable for imaging in electrostatographic copiers.